One significant problem with heat pumps is a possible system malfunction whereby the room thermostat in the room to be heated and/or cooled by the heat pump commands compressor operation so as to either heat or cool the space but the compressor either does not operate or, in some cases, cycles on and off. Another system malfunction is where the compressor is energized and running but is not compressing the refrigerant; this is exemplified by the compressor valve failures and/or the loss of refrigerant. There are no obvious indications of these faults to a person near the thermostat because the compressor is at a location remote from that of the thermostat. This, in turn, with many systems, can mean (when the thermostat is calling for heating of the building) that auxiliary electric resistance heating is automatically used to heat the building; i.e., a backup heating system; however, this usually results in a much higher cost of heating. Accordingly, various prior art schemes have been devised for attempting to detect whether or not the compressor is running, or is running without refrigerant in the system, but all of these prior art arrangements have one or more shortcomings. For example, one prior scheme is to use the pressure of the refrigerant at the discharge side of the compressor; however, this does not provide a reliable enough signal. Also, it has been proposed that the value or magnitude of the electric current and/or electric voltage energizing the motor driving the compressor be monitored; however, these schemes only indicate that the motor is being powered and do not confirm that the compressor is actually pumping refrigerant.
An object of the present invention is to provide a new and significantly improved compressor fault detection system for a reverse cycle refrigeration system.